Characterization of Macrocycles Formed from Cationic Copolymerization of Tetrahydrofuran with Propylene Oxide by GPC and GC/MS

Abstract

The copolymers obtained from a THF/PO-BF₃O(C₂H₅)₅-glycerin-ethylene chloride cationic copolymerization system were analyzed by GPC. The chromatograms show two groups of peaks, one located in the high molecular weight (MW) region and the other in the low MW region. In order to examine the low MW region in detail, the oligomers were separated from the copolymer by distillation under high vacuum, and further identified by GC/MS, NMR. It was found that these were an expected series of cyclic oligomers, i.e., PO:THF crown ethers: 1:2, 3:1, 2:2, 1:3, 3:2, 2:3, 1:4, 4:2, 3:3, 2:4, 4:3. Through the study of the elution behavior of these crown ethers in toluene with GPC, a linear relationship of the elution time against the logarithm of their MW's was obtained. Under the same GPC conditions, the relationship between the elution time and MW of n-alkanes was also determined. It was found that the hydrodynamic volume of the crown ethers is less than that of the n-alkanes with same MW, and they can be treated as homologous series as in the case of n-alkanes on the study of GPC elution behavior ignoring the influence of PO:THF composition ratios in crown ether rings.